1. Field of the Invention
The present invention relates to a two-cycle internal combustion engine capable of preventing a blow-by phenomenon of a mixture in a combustion chamber thereby improving fuel economy and attaining better exhaust gas purifying performance.
2. Description of Background Art
In a related art, fuel supplied by a carburetor to a two-cycle internal combustion engine is mixed with intake air and the resulting mixture is sucked into a crank chamber and is then supplied into a combustion chamber through a scavenging port. In this case, since the timing of the opening an exhaust port is set earlier than that of the scavenging port (an upper edge of the exhaust port is higher than that of the scavenging port), the mixture fed into the combustion chamber is discharged into an exhaust passage, thus easily causing a so-called blow-by phenomenon.
Although the blow-by phenomenon is suppressed by an exhaust pulsating effect in an exhaust chamber, it is difficult for the suppression to cover the whole operation range, resulting in that both the fuel economy and exhaust purifying performance are affected.
In an effort to solve the above-mentioned problem, two-cycle internal combustion engines have been proposed in Japanese Patent Laid-open Nos. Hei 3-100318 and Hei 5-302521.
In the two-cycle internal combustion engine disclosed in Japanese Patent Laid-open No. Hei 3-100318, a high pressure chamber is connected to a crank chamber through a check valve, the high pressure chamber is connected to the combustion chamber through an air passage, a solenoid valve is disposed in the lower end of the air passage, and a fuel injection valve capable of injecting fuel towards the combustion chamber is provided at the upper end of the air passage.
In the two-cycle internal combustion engine disclosed in Japanese Patent Laid-open No. Hei 5-302521, a chamber is formed in a position adjacent to both the crankcase and the cylinder block, an intake control valve is interposed between a crank chamber and said chamber, a scavenging control valve is interposed between said chamber and a combustion chamber in a cylinder, and a fuel injection valve is provided for injection of fuel toward said chamber.
In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 3-100318, with respect to the fuel injected from the fuel injection valve, part of the fuel deposited in the air passage falls by gravity, entering the crank chamber through a check valve disposed at the bottom of the air passage, and flows in a state wherein the fuel is atomized into the combustion chamber from the crank chamber through another scavenging port. As a result, it is difficult to sufficiently prevent the blow-by phenomenon and to obtain a stable combustion. Further, it is difficult to suitably control the amount of fuel fed into the combustion chamber, resulting in degraded responsiveness.
In the two-cycle internal combustion engine described in Japanese Patent Laid-open No. Hei 5-302521, all of the intake air in the crank chamber is introduced through the intake control valve and is mixed with the fuel introduced into the chamber through the fuel injection valve. The resulting mixture flows into the combustion chamber through the scavenging control valve. Accordingly, the two-cycle internal combustion engine is not configured so as to permit only air to flow from the crank chamber into the combustion chamber through a scavenging port, and hence the blow-by phenomenon is unavoidable. Further, although an upstream side of the scavenging control valve is opened to the lower portion of said chamber, the opening position thereof is not the lowest, so that the fuel injected into said chamber remains at the bottom of said chamber, thus giving rise to a problem that the amount of fuel fed into the combustion chamber cannot be accurately proportional to the amount of fuel injected from the fuel injection valve, resulting in degraded responsiveness.